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Asked: 2026-05-27T02:29:54+00:00

I am trying to load and draw a 2d texture using OpenGL with GLFW

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I am trying to load and draw a 2d texture using OpenGL with GLFW and SOIL. I have this code, but I only get one solid color (which seems to come from the texture).

I have tested whether the .png loads with an example that came with SOIL, and it worked fine so there has to be some issue in my code.

This is my code:

#include <cstdio>

#include "GL/glfw.h"
#include "SOIL.h"

// function declarations
void drawscene();
void idlefunc();
void updatedisplay();

// global data
GLuint texture; // our example texture

int main(int argc, char **argv) {
    if (!glfwInit()) {
        fprintf(stderr, "Failed to initialize GLFW\n");
        return 1;
    }

    if (!glfwOpenWindow(640, 480, 0, 0, 0, 0, 16, 0, GLFW_WINDOW)) {
        fprintf(stderr, "Failed to open GLFW window\n");
        return 1;
    }

    // enable vsync (if available)
    glfwSwapInterval(1);

    // load textures
    texture = SOIL_load_OGL_texture(
        "tex.png",
        SOIL_LOAD_AUTO,
        SOIL_CREATE_NEW_ID,
        SOIL_FLAG_POWER_OF_TWO | SOIL_FLAG_MIPMAPS | SOIL_FLAG_DDS_LOAD_DIRECT
    );

    // check for an error during the texture loading
    if (!texture) {
        printf("SOIL loading error: '%s'\n", SOIL_last_result());
    }

    while (glfwGetWindowParam(GLFW_OPENED)) {
        idlefunc();
    }

    // if we get here something went wrong
    return 0;
}

// this function gets called every frame
void idlefunc() {
    updatedisplay();
    drawscene();
}

// set up te display
void updatedisplay() {
    int screen_width, screen_height;
    glfwGetWindowSize(&screen_width, &screen_height);

    if (screen_height <= 0) screen_height = 1;
    if (screen_width <= 0) screen_width = 1;

    glViewport(0, 0, screen_width, screen_height);

    glClearColor(0.02f, 0.02f, 0.02f, 0.0f);
    glClear(GL_COLOR_BUFFER_BIT);

    glEnable(GL_TEXTURE_2D);
    glDisable(GL_DEPTH_TEST);

    glMatrixMode(GL_PROJECTION);
    glLoadIdentity();
    glOrtho(0.0, screen_width, screen_height, 0.0, 0.0, 1.0);

    glMatrixMode(GL_MODELVIEW);
    glLoadIdentity();

    // displacement trick for exact pixelization
    glTranslatef(0.375f, 0.375f, 0.0f);
}

// draw the scene in this function
void drawscene() {
    glBindTexture(GL_TEXTURE_2D, texture);
    glPushMatrix();
        glTranslatef(10.0f, 10.0f, 0);
        glBegin(GL_QUADS);
            glTexCoord2f(0.0f, 0.0f);
            glVertex2f(0.0f, 0.0f);
            glTexCoord2f(0.0f, 128.0f);
            glVertex2f(0.0f, 128.0f);
            glTexCoord2f(128.0f, 128.0f);
            glVertex2f(128.0f, 128.0f);
            glTexCoord2f(128.0f, 0.0f);
            glVertex2f(128.0f, 0.0f);
        glEnd();
    glPopMatrix();

    glfwSwapBuffers();
}
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1 Answer

  1. Editorial Team

    Found the issue (thanks to user786653). No matter the vertex coords, the tex coords are between 0.0 and 1.0. This is the fixed code:

    // draw the scene in this function
void drawscene() {
    glBindTexture(GL_TEXTURE_2D, texture);
    glPushMatrix();
        glTranslatef(10.0f, 10.0f, 0);
        glBegin(GL_QUADS);
            glTexCoord2f(0.0f, 0.0f);
            glVertex2f(0.0f, 0.0f);
            glTexCoord2f(0.0f, 1.0f);
            glVertex2f(0.0f, 128.0f);
            glTexCoord2f(1.0f, 1.0f);
            glVertex2f(128.0f, 128.0f);
            glTexCoord2f(1.0f, 0.0f);
            glVertex2f(128.0f, 0.0f);
        glEnd();
    glPopMatrix();

    glfwSwapBuffers();
}
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